The present disclosure relates to clutches including friction plates, separator plates, a clutch hub, and a piston, and speed change devices including the same.
Conventionally, a clutch including a clutch hub having a tubular portion on which the inner peripheral portions of a plurality of separator plates are fitted and an annular coupling portion extended radially inward from the tubular portion is known as this type of clutch (see, e.g., Japanese Patent Application Publication No. 2015-105723). In this clutch, the inner peripheral portion of the coupling portion of the clutch hub is constantly coupled (fixed) via splines to a shaft portion extended in the axial direction from a sun gear of a planetary gear forming a speed change device. An oil chamber defining member that together with a piston defines an engagement oil chamber is fixed to the shaft portion of the sun gear by using a snap ring. The piston is supported by the shaft portion so that the piston rotates with the shaft portion of the sun gear and can move in the axial direction. The piston together with the clutch hub and the shaft portion defines a centrifugal oil pressure cancel chamber in which a centrifugal oil pressure generated in the engagement oil chamber is canceled. The sun gear that is an element to be connected by the clutch rotates at a relatively high speed when the speed change device is in operation. By defining all the oil chambers of the clutch, namely the engagement oil chamber and the centrifugal oil pressure cancel chamber, by the shaft portion, the piston, and the oil chamber defining member that rotate with the sun gear, hydraulic oil is restrained from flowing out of the centrifugal oil pressure cancel chamber once supplied, and shift performance of the speed change device can be improved.